Study On The Biodiversity And Abundance Of Comammox Bacteria In The Rhizosphere Of Emergent Macrophytes Of Lake Liangzi And Lake Yue

Nitrification is a key component of the biogeochemical cycle.It is usually considered a two-step process,where ammonia is first oxidized to nitrite and then to nitrate.Recent studies have shown that the newly discovered complete ammonia oxidizer?Comammox?can independently complete the ammonia oxidation and nitrite oxidation processes.At present,there is a lack of research on the Comammox bacteria in the rhizosphere of emergent plants in riparian zone ecosystems.In this paper,the rhizosphere of emergent plants in the riparian zone of Lake Liangzi and Lake Yuehu was chose as the research object.Specific primers were used for cloning,sequencing and quantitative PCR to study the community structure and abundance of Comammox bacteria in the lake,the coexistence of AOA?Ammonia Oxidizing Archaea??AOB?Ammonia Oxidizing Bacteria?and Comammox bacteria and the impact of environmental factors on the diversity and abundance of Comammox bacteria,to get a deeper understanding of the nitrogen cycle in lakes and provide a theoretical basis for the restoration of eutrophication.The main findings were as follows:?1?By cloning,sequencing and quantitative PCR of the Comammox bacteria in the sediments of Lake Liangzi and Lake Yuehu,the sequences of the Comammox bacteria were successfully amplified in the sediments of the riparian zone.The widespread presence of bacteria in the rhizosphere of emergent plants in the riparian zone of Lake Liangzi and Lake Yuehu provides a strong basis for confirming the widespread distribution of Comammox bacteria in the lake environment.The abundance range of Comammox bacteria in the Lake Liangzi sediment is 10⁶-10⁸ copies g^-1 dry sediment,and the abundance range of the bacteria measured in the Lake Yuehu sediment is 10⁴-10⁶ copies g^-1 dry sediment,which are different from the current reports.The range of the bacteria in the environmental samples is relatively similar,and the abundance of Comammox in different sampling points in different ecological environments shows spatial heterogeneity with this study.The abundance of AOA and AOB in the sediments of Lake Liangzi is lower than that of Comammox bacteria,and the mean value of AOB abundance in the sediments of Lake Yuehu is higher than that of Comammox bacteria.It shows that Comammox is more competitive in the environment of the rhizosphere sediments of emerging plants in Liangzi Lake,and AOB is more competitive in Lake Yuehu.?2?Phylogenetic tree analysis showed that the main Comammox in the rhizosphere sediments of emerging plants in Lake Liangzi and Lake Yuehu had a relatively complex community structure,clustered into multiple branches.They are similar to sequences from multiple environmental sources,all of which are Candidatus Nitrospira.The Lake Liangzi sediments are highly similar to Candidatus Nitrospira nitrosa.Candidatus Nitrospira inopinata is the main dominant group in Lake Yuehu sediments.?3?Redundancy analysis showed that the Comammox of each sampling point in Lake Liangzi had a negative correlation with AOA and AOB,and the abundance of Comammox had a positive correlation with sediment p H,OM,TP,TN,NO₂^--N,NO₃^--N.There was no significant correlation between Comammox bacteria and AOB at each sampling point in Lake Yuehu,and the abundance of Comammox bacteria was positively correlated with sediment NO₂^--N,NH₄⁺-N and p H.Different lake environments affect the abundance of Comammox bacteria and produce certain differences.For Lake Liangzi,the average abundance of the Comammox bacteria in rhizosphere is lower than non-rhizosphere and far-rhizosphere.For Lake Yue,the abundance of the Comammox bacteria in rhizosphere are higher than non-rhizosphere in four different emergent plants,indicating that different environment and emergent plants are selective for Comammox.